NbO Nanolithography with an Atomic Force Microscope

The Josephson junctions (JJs) in superconducting qubits are commonly made out of an AlO_x insulator sandwiched between superconducting Al layers. However, Al/AlO_x/Al JJs host two-level system losses at their metal-oxide interfaces. All-oxide JJs are a promising solution to this problem. One candidate oxide system is NbO, a stoichiometric oxide known to exhibit bulk superconductivity [1]. In order to pattern the material and test devices, a simple nanolithography technique is needed. We investigate local oxidation as a technique to etch thin-film NbO. To do this, we use a conducting atomic force microscope (C-AFM) for rapid prototyping, enabling development of a new JJ architecture.

[1] Okaz, A. M. & Keesom, P. H. Specific heat and magnetization of the superconducting monoxides: NbO and TiO. Phys. Rev. B 12, 4917–4928 (1975).